Non-aqueous electrochemical cells

ABSTRACT

Electrochemical cells are disclosed. In some embodiments, an electrochemical cell includes a cathode having less than about 2,000 ppm of water, an anode, and an electrolyte having a first lithium salt and LiPF 6 .

TECHNICAL FIELD

The invention relates to non-aqueous electrochemical cells.

BACKGROUND

Batteries or electrochemical cells are commonly used electrical energysources. A battery contains a negative electrode, typically called theanode, and a positive electrode, typically called the cathode. The anodecontains an active material that can be oxidized; the cathode containsor consumes an active material that can be reduced. The anode activematerial is capable of reducing the cathode active material.

When a battery is used as an electrical energy source in a device,electrical contact is made to the anode and the cathode, allowingelectrons to flow through the device and permitting the respectiveoxidation and reduction reactions to occur to provide electrical power.An electrolyte in contact with the anode and the cathode contains ionsthat flow through the separator between the electrodes to maintaincharge balance throughout the battery during discharge.

SUMMARY

In one aspect, the invention features an electrochemical cell, includinga cathode having less than about 2,000 ppm of water, an anode, and anelectrolyte containing a first lithium salt and LiPF₆. By restrictingthe water content of the cathode, the occurrence of LiPF₆ hydrolyzing toform hydrofluoric acid, a highly corrosive agent, is reduced.

At the same time, the cell has good performance, for example, at lowtemperatures, after freshly produced, and/or after prolonged storage atelevated temperatures. The electrochemical cell is capable of having awide range of voltage stability and high conductivity. In embodiments,such as those that include aluminum component(s), LiPF₆, with or withoutother electrolyte components, is capable of reducing corrosion of thecomponent(s). The electrolyte is relatively inexpensive.

In another aspect, the invention features an electrochemical cell,including a cathode having manganese oxide, the cathode having less thanabout 2,000 ppm of water; an anode including lithium; and an electrolyteincluding lithium trifluoromethanesulfonate and LiPF₆ salts.

Aspects of the invention may include one or more of the followingfeatures. The cathode can have less than about 1,500 ppm of water, suchas less than about 1,000 ppm of water, or less than about 500 ppm ofwater. The cathode can include manganese oxide. The anode can includelithium. The cell can be a primary cell.

Various embodiments of the electrolyte can be used. The first lithiumsalt can include lithium trifluoromethanesulfonate, such as, in molefraction, from about 5% to about 95% of the lithiumtrifluoromethanesulfonate. The electrolyte can further include a thirdlithium salt, such as LiClO₄ and/or lithium-bis(oxalato)borate. Theelectrolyte can include from about 300 to about 10,000 ppm of LiClO₄.The cell can further include an aluminum surface. The electrolyte canfurther include ethylene carbonate, propylene carbonate,dimethoxyethane, and/or butylene carbonate. The electrolyte can furtherinclude propylene carbonate and dimethoxyethane, such as from about 30%to about 90% by weight of dimethoxyethane. The electrolyte can include,by weight, from about 5% to about 30% of ethylene carbonate, and fromabout 30% to about 90% dimethoxyethane. The electrolyte can furtherinclude ethylene carbonate, butylene carbonate, and dimethoxyethane,such as, by weight, from about 5% to about 30% of ethylene carbonate,and from about 30% to about 90% of dimethoxyethane. The electrolyte caninclude dioxolane.

In another aspect, the invention features a method including dischargingan electrochemical cell including a cathode having manganese oxide, thecathode having less than about 2,000 ppm of water, an anode comprisinglithium, and an electrolyte containing lithium trifluoromethanesulfonateand LiPF₆ salts; and disposing the cell without recharging the cell.

Other aspects, features, and advantages are in the description,drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a nonaqueous electrochemical cell.

FIG. 2 is a graph showing load voltage versus number of cycles for testcells under a “digital camera” test at room temperature.

FIG. 3 is a graph showing load voltage versus number of cycles for testcells under a “digital camera” test at zero degrees Celsius.

FIG. 4 is a graph showing load voltage versus efficiency for fresh coincells having aluminum cathode screens under a 100 Ohm (1.5 mA)simulation.

FIG. 5 is a graph showing load voltage versus efficiency for fresh testcells having aluminum cathode screens under an HEC (60 mA pulse)simulation.

FIG. 6 is a graph showing load voltage versus efficiency for stored testcells having aluminum cathode screens under an HEC (60 mA pulse)simulation.

DETAILED DESCRIPTION

Referring to FIG. 1, an electrochemical cell 10 (such as a primarylithium cell) includes an anode 12 in electrical contact with a negativelead 14, a cathode 16 in electrical contact with a positive lead 18, aseparator 20 and an electrolytic solution. Anode 12, cathode 16,separator 20 and the electrolytic solution are contained within a case22. The electrolytic solution includes a solvent system and a salt thatis at least partially dissolved in the solvent system. Electrochemicalcell 10 further includes a cap 24 and an annular insulating gasket 26,as well as a safety valve 28.

The electrolytic solution or electrolyte can be in liquid, solid or gel(e.g., polymer) form. The electrolyte can contain an organic solventsuch as propylene carbonate (PC), ethylene carbonate (EC),dimethoxyethane (DME), butylene carbonate (BC), dioxolane (DO),tetrahydrofuran (THF), acetonitrile (CH₃CN), gamma-butyrolactone,diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methylcarbonate (EMC), dimethylsulfoxide (DMSO), methyl acetate (MA), methylformiate (MF), sulfolane, or combinations thereof. The electrolyte canalternatively contain an inorganic solvent such as SO₂ or SOCl₂. Theelectrolyte also can contain one or more lithium salts, such as lithiumtrifluoromethanesulfonate (LiTFS), LiPF₆, lithium-bis(oxalato)borate(LiBOB), and/or LiClO₄.

In preferred embodiments, the electrolyte includes a salt mixture havingLiTFS and LiPF₆. The total concentration of salts in the mixture ofsolvent(s) can range from about 0.3 M to about 1.2 M. The totalconcentration of LiTFS and LiPF₆ in the mixture of solvent(s) can beequal to or greater than about 0.30 M, 0.35 M, 0.40 M, 0.45 M, 0.50 M,0.55 M, 0.60 M, 0.65 M, 0.70 M, 0.75 M, 0.80 M, 0.85 M, 0.90 M, 0.95 M,1.00 M, 1.05 M, 1.10 M, or 1.15 M; and/or equal to or greater than about1:2 M, 1.15 M, 1.10 M, 1.05 M, 1.00 M, 0.95 M, 0.90 M, 0.85 M, 0.80 M,0.75 M, 0.70 M, 0.65 M, 0.60 M, 0.55 M, 0.50 M, 0.45 M, 0.40 M, or0.35M. Of the total concentration of LiTFS and LiPF₆ salts, theconcentration of LiTFS in the mixture of solvents can be (in molefraction) from about five percent to about 95 percent. For example, theconcentration of LiTFS in the mixture of solvents can be (in molefraction) equal to or greater than five percent, ten percent, 15percent, 20 percent, 25 percent, 30 percent, 35 percent, 40 percent, 45percent, 50 percent, 55 percent, 60 percent, 65 percent, 70 percent, 75percent, 80 percent, 85 percent, or 90 percent; and/or equal to or lessthan 95 percent, 90 percent, 85 percent, 80 percent, 75 percent, 70percent, 65 percent, 60 percent, 55 percent, 50 percent, 45 percent, 40percent, 35 percent, 30 percent, 25 percent, 20 percent, 15 percent, orten percent. The concentration of LiPF₆ in the mixture of solvents canbe equal to 100 percent minus the concentration of LiTFS in the mixtureof solvents. For example, if the total concentration of salt in themixture of solvents is 0.5 M, and the LiTFS concentration (in molefraction) in the mixture of solvents is 90 percent (i.e., 0.45 M), thenthe LiPF₆ concentration in the electrolyte mixture is ten percent (i.e.,0.05 M).

In some embodiments, the electrolyte further includes one or more othersalts. For example, the electrolyte can further include other lithiumsalts, such as LiClO₄ and/or LiBOB. Lithium perchlorate (LiClO₄) canreduce (e.g., inhibit or suppress) the occurrence of corrosion, such aswhen cell 10 includes an aluminum component (e.g., an aluminum cathodecurrent collector) or an aluminum couple. A couple generally includes atleast two metal or metal alloy surfaces that are in electrical contactwith each other. As an example, cathode 16 can include an aluminumcurrent collector that is in electrical contact with positive lead 18,which can be made of steel. The two metal surfaces that are inelectrical contact with each other can have the same composition (e.g.,both surfaces can be made of the same metal or metal alloy (e.g., bothsurfaces are made of aluminum)), or can have different compositions(e.g., the two surfaces can be made of different metals or metal alloys(e.g., one surface is made of aluminum and the other surface is made ofan alloy of aluminum)). A surface can have an interface between twoportions having the same composition. The interface can have a differentcomposition than the portions, e.g., due to wetting and diffusion. Insome embodiments, the electrolyte includes from about 300 ppm to about10,000 ppm (relative to electrolyte) of a third salt (e.g., LiClO₄) inaddition to LiTFS and LiPF₆. The electrolyte can include equal to orgreater than about 300 ppm, 1,000 ppm, 2,000 ppm, 3,000 ppm, 4,000 ppm,5,000 ppm, 6,000 ppm, 7,000 ppm, 8,000 ppm, or 9,000 ppm of the thirdsalt; and/or less than or equal to about 10,000 ppm, 9,000 ppm, 8,000ppm, 7,000 ppm, 6,000 ppm, 5,000 ppm, 4,000 ppm, 3,000 ppm, 2,000 ppm,or 1,000 ppm of the third salt.

In addition to the salts, the electrolyte includes a mixture of one ormore solvents. Examples of solvent mixtures include DME and PC; EC, PC,and DME; EC, BC, and DME; and dioxolane. In a mixture of solvents havingDME and PC, the concentration of DME in the mixture of solvents canrange from about 30 percent to about 90 percent by weight. Theconcentration of DME in the mixture of solvents can be equal to orgreater than about 30 percent, 35 percent, 40 percent, 45 percent, 50percent, 55 percent, 60 percent, 65 percent, 70 percent, 75 percent, 80percent by weight, or 85 percent by weight; and/or equal to or less thanabout 90 percent, 85 percent, 80 percent, 75 percent, 70 percent, 65percent, 60 percent, 55 percent, 50 percent, 45 percent, 40 percent, or35 percent by weight. The concentration of PC in the mixture of solventscan be equal to 100 percent minus the concentration of DME. For example,if the concentration of DME in the mixture of solvents is 75 percent byweight, then the concentration of PC in the mixture of solvents is 25percent by weight. If the concentration of DME in the mixture ofsolvents is 50-75 percent by weight, then the concentration of PC in themixture of solvents is 25-50 percent by weight.

In a mixture of solvents including EC, DME and PC, the concentration ofEC in the mixture of solvents can be from about five percent to about 30percent by weight. The concentration of EC in the mixture of solventscan be equal to or greater than five percent, ten percent, 15 percent,20 percent, or 25 percent by weight; and/or equal to or less than 30percent, 25 percent, 20 percent, 15 percent, or ten percent by weight.The concentration of DME in the mixture of solvents can range from about30 percent to about 90 percent by weight. The concentration of DME inthe mixture of solvents can be equal to or greater than 30 percent, 35percent, 40 percent, 45 percent, 50 percent, 55 percent, 60 percent, 65percent, 70 percent, 75 percent, 80 percent, or 85 percent by weight;and/or equal to or less than about 90 percent, 85 percent, 80 percent,75 percent, 70 percent, 65 percent, 60 percent, 55 percent, 50 percent,45 percent, 40 percent, or 35 percent by weight. The concentration of PCin the mixture of solvents can be equal to 100 percent minus theconcentration of EC and DME. For example, if the concentration of EC inthe mixture of solvents is 15 percent by weight, and the concentrationof DME in the mixture of solvents is 60 percent by weight, then theconcentration of PC in the mixture of solvents is 25 percent by weight.Examples of an EC:DME:PC solvent mixture are 14:62:24 and 10:75:15percent by weight.

A mixture of solvents including EC:BC:DME can have generally the sameconcentrations described above as for EC:PC:DME, respectively.

Cathode 16 includes an active cathode material, which is generallycoated on the cathode current collector. The current collector caninclude a steel, such as a stainless steel (e.g., a series 200 stainlesssteel, a 300 series stainless steel, a 400 series stainless steel, orcold rolled steel); aluminum (e.g., in the form of an aluminum foil); analloy including aluminum; titanium; or nickel. In some embodiments, thecurrent collector can be a metal grid. The current collector generallyhas at least one dimension (e.g., a length, a width, and/or a diameter)that is greater than about 0.2 millimeter (e.g., greater than about 0.5millimeter, greater than about one millimeter, greater than about 1.5millimeters, greater than about two millimeters). The active materialcan be, e.g., a metal oxide, a halide, or a chalcogenide; alternatively,the active material can be sulfur, an organosulfur polymer, or aconducting polymer. Specific examples include manganese oxides (such asMnO₂), cobalt oxides, manganese spinels, V₂O₅, CoF₃, molybdenum-basedmaterials such as MoS₂ and MoO₃, FeS₂, SOCl₂, S, and (C₆H₅N)_(n) and(S₃N₂)_(n), where n is at least two. The active material can also be acarbon monofluoride. An example is a compound having the formula CF_(x),where x is from 0.5 to one, or higher. The active material can be mixedwith a conductive material such as carbon and a binder such aspolytetrafluoroethylene (PTFE) or Kraton (available from Shell). Anexample of a cathode is one that includes aluminum foil coated withMnO₂. The cathode can be prepared as described in U.S. Pat. No.4,279,972. Specific cathode materials are a function of, e.g., the typeof cell (such as primary or secondary).

In preferred embodiments, cathode 16 contains a low amount of water.Without wishing to be bound by theory, it is believed that in thepresence of water, LiPF₆ hydrolyzes to form hydrofluoric acid, whichtends to corrode the components of cell 10 at an accelerated rate. Byreducing the amount of water in cathode 16, the formation ofhydrofluoric acid is reduced, thereby enhancing the performance of cell10. In some embodiments, cathode 16 includes less than about 2,000 ppmof water. For example, cathode 16 can include less than about 1,500 ppm,1,000 ppm, or 500 ppm of water. In comparison, certain cathodematerials, such as manganese dioxide, can contain up to 2% by weightwater. The amount of water in cathode 16 can be controlled, for example,by only exposing the cathode to dry environments, such as a dry box,and/or by heating the cathode material (e.g., at about 200° C. undervacuum). Manganese oxide cathode material is available from, forexample, Kerr McGee, Delta, or ChemMetals. In some embodiments, thewater content in cell 10 can be slightly higher than the water contentof cathode 16, such as when the electrolyte contains a small amount ofwater (e.g., a maximum of about 50 ppm).

As used herein, the water content of cathode 16 is determinedexperimentally using standard Karl Fisher titrimetry. For example,moisture detection can be performed using a Mitsubishi moisture analyzer(such as CA-05 or CA-06) with a pyrolizing unit (VA-05 or VA-21) set at110-115° C.

Anode 12 can include an active anode material, usually in the form of analkali metal (e.g., lithium, sodium, potassium) or an alkaline earthmetal (e.g., calcium, magnesium). The anode can include an alloy of analkali metal (e.g., lithium) and an alkaline earth metal or an alloy ofan alkali metal and aluminum. The anode can be used with or without asubstrate. The anode also can include an active anode material and abinder. In this case an active anode material can include tin-basedmaterials, carbon-based materials, such as carbon, graphite, anacetylenic mesophase carbon, coke, a metal oxide and/or a lithiatedmetal oxide. The binder can be, for example, PTFE. The active anodematerial and binder can be mixed to form a paste which can be applied tothe substrate of anode 12. Specific anode materials are a function of,for example, the type of cell (such as primary or secondary).

Separator 20 can be formed of any of the standard separator materialsused in electrochemical cells. For example, separator 20 can be formedof polypropylene (e.g., nonwoven polypropylene or microporouspolypropylene), polyethylene, a polysulfone, or combinations thereof.

Case 22 can be made of a metal (e.g., aluminum, an aluminum alloy,nickel, nickel plated steel) or a plastic (e.g., polyvinyl chloride,polypropylene, polysulfone, ABS or a polyamide).

Positive lead 18 and/or cap 24 can be made of, for example, aluminum,nickel, titanium, or steel.

Electrochemical cell 10 can be a primary cell or a secondary cell.Primary electrochemical cells are meant to be discharged, e.g., toexhaustion, only once, and then discarded. Primary cells are notintended to be recharged. Primary cells are described, for example, inDavid Linden, Handbook of Batteries (McGraw-Hill, 2d ed. 1995).Secondary electrochemical cells can be recharged for many times, e.g.,more than fifty times, more than a hundred times, or more. In somecases, secondary cells can include relatively robust separators, such asthose having many layers and/or that are relatively thick. Secondarycells can also be designed to accommodate for changes, such as swelling,that can occur in the cells. Secondary cells are described, e.g., inFalk & Salkind, “Alkaline Storage Batteries”, John Wiley & Sons, Inc.1969; U.S. Pat. No. 345,124; and French Patent No. 164,681, all herebyincorporated by reference.

To assemble the cell, separator 20 can be cut into pieces of a similarsize as anode 12 and cathode 16, and placed between the electrodes, asshown in FIG. 1. Anode 12, cathode 16, and separator 20 are then placedwithin case 22, which is then filled with the electrolytic solution andsealed. One end of case 22 is closed with cap 24 and annular insulatinggasket 26, which can provide a gas-tight and fluid-tight seal. Positivelead 18 connects cathode 16 to cap 24. Safety valve 28 is disposed inthe inner side of cap 24 and is configured to decrease the pressurewithin electrochemical cell 10 when the pressure exceeds somepredetermined value. Additional methods for assembling the cell aredescribed in U.S. Pat. Nos. 4,279,972; 4,401,735; and 4,526,846.

Other configurations of electrochemical cell 10 can also be used,including, e.g., the coin cell configuration. The electrochemical cellscan be of different voltages, e.g., 1.5 V, 3.0 V, or 4.0 V.

The invention is further described in the following examples, which donot limit the scope of the invention described in the claims. In theexamples, the cells were assembled using the procedures described inU.S. Ser. No. 10/719,056; U.S. Ser. No. 10/719,025; and U.S. Ser. No.10/719,014, all filed Nov. 24, 2003, and all incorporated by reference.

EXAMPLE 1

Referring to FIG. 2, a graph showing voltage under highest power loadversus number of cycles for test cells under a “digital camera” test atroom temperature is shown. The digital camera test is used to simulateworking conditions of a digital camera. The test includes subjecting thetest cells to a number of pulses under constant power withdrawal andmeasuring voltage. The test was performed using an Arbin testing system,available from Arbin Co.

Test cells including LiTFS/LiPF₆ salts were compared with test cellsincluding LiTFS/LiTFSI. Ten 2/3A cells filled with a battery gradeelectrolyte, supplied by Ferro Co., having 0.54M LiTFS and 0.36M LiPF₆salts were tested. For comparison, ten 2/3A cells filled with anelectrolyte (battery grade), supplied by Ferro Co., having 0.54M LiTFSand 0.36M LiTFSI salts were used as control cells.

As shown in FIG. 2, the cells including 0.54M LiTFS and 0.36M LiPF₆salts exhibited performance similar to the control cells. Correspondingperformance data for the digital camera test at room temperature atdifferent voltage cutoffs (VCO) are presented in a Table 1.

TABLE 1 Capacity (Fresh) Test Electrolyte Cycle Ah RT, 2.0 VCO 0.54MLiTFS, 0.36M LiTFSI 130 0.892 0.54M LiTFS, 0.36M LiPF₆ 135 0.921 RT, 1.7VCO 0.54M LiTFS, 0.36M LiTFSI 161 1.131 0.54M LiTFS, 0.36M LiPF₆ 1631.136 RT, 1.5 VCO 0.54M LiTFS, 0.36M LiTFSI 168 1.182 0.54M LiTFS, 0.36MLiPF₆ 168 1.180

EXAMPLE 2

Referring to FIG. 3, a graph showing voltage under highest power loadversus number of cycles for test cells under the digital camera test atzero degrees Celsius is shown.

Test cells including LiTFS/LiPF₆ salts were compared with test cellsincluding LiTFS/LiTFSI salts. Ten 2/3A cells filled with a battery gradeelectrolyte, supplied by Ferro Co., having 0.54M LiTFS and 0.36M LiPF₆salts were tested. For comparison, ten 2/3A cells filled with anelectrolyte (battery grade), supplied by Ferro Co., having 0.54M LiTFSand 0.36M LiTFSI salts were used as control cells.

As shown in FIG. 3, the cells including 0.54M LiTFS and 0.36M LiPF₆salts exhibited performance similar to the control cells. Correspondingperformance data for the digital camera test at zero degrees Celsius atdifferent voltage cutoffs (VCO) are presented in Table 2.

TABLE 2 Capacity (Fresh) Test Electrolyte Cycle Ah 0° C., 2.0 VCO 0.54MLiTFS, 0.36M LiTFSI 32 0.227 0.54M LiTFS, 0.36M LiPF₆ 33 0.233 0° C.,1.7 VCO 0.54M LiTFS, 0.36M LiTFSI 118 0.889 0.54M LiTFS, 0.36M LiPF₆ 1120.842 0° C., 1.5 VCO 0.54M LiTFS, 0.36M LiTFSI 130 0.987 0.54M LiTFS,0.36M LiPF₆ 128 0.981

EXAMPLE 3

Referring to FIG. 4, a graph showing running voltage versus efficiencyfor fresh coin cells having an aluminum screen as a cathode currentcollector under a 100 Ohm coin cell test is shown. The 100 Ohm coin celltest is used to simulate conditions of a 100 Ohm test for 2/3A cells.The test includes subjecting the test cells to constant currentdischarge (current is scaled down based on active material weight in acathode) and measuring voltage. The test was performed using an Arbintesting system, available from Arbin Co.

Test cells including LiTFS/LiPF₆/LiClO₄ salts were compared with testcells including LiTFS/LiClO₄ salts and test cells including LiPF₆ salts.Ten 2430 coin cells filled with an electrolyte (battery grade) suppliedby Ferro Co. having 0.54M LiTFS, 0.36M LiPF₆, and 0.025% by weightLiClO₄ were tested. The LiClO₄ salt was added to the electrolyte tosuppress corrosion of aluminum. For comparison, ten 2430 coin cellsfilled with an electrolyte (battery grade) supplied by Ferro Co. having1 M LiPF₆ salt were also tested. Ten 2430 coin cells filled with anelectrolyte (battery grade) supplied by Ferro Co. having 0.64M LiTFS and0.025% by weight LiClO₄ salts were used as control cells.

As shown in FIG. 4, the 2430 coin cells including 0.54M LiTFS, 0.36MLiPF₆, 0.025% by weight LiClO₄ and 1 M LiPF₆ exhibited performancesimilar to the control cells. Efficiency was calculated as a ratio ofdelivered capacity to a theoretical capacity. Corresponding performancedata for 100 Ohm simulation test at different voltage cutoffs (VCO) arepresented in a Table 3.

TABLE 3 Efficiency, % Efficiency, % Electrolyte (2.0 VCO) (1.5 VCO)0.64M LiTFS, 0.025% by weight 88.87 92.81 LiClO₄ 0.54M LiTFS, 0.36MLiPF₆, 91.21 94.93 0.025% by weight LiClO₄ 1M LiPF₆ 90.29 93.75

EXAMPLE 4

Referring to FIG. 5, a graph showing voltage under highest current loadversus efficiency for fresh coin cells having an aluminum screen as acathode current collector under a HEC (60 mA pulse) simulation test isshown. The HEC (60 mA pulse) simulation test is used to simulateconditions corresponding to a high power HEC (high end camera) test for2/3A cells. The test includes subjecting the test cells to number ofpulses under constant current (3 second pulse, 7 second rest), andmeasuring voltage. The test was performed using an Arbin testing system,available from Arbin Co.

Test cells including LiTFS/LiPF₆/LiClO₄ salts were compared with testcells including LiTFS/LiClO₄ salts and test cells including LiPF₆ salt.Ten 2430 coin cells filled with an electrolyte (battery grade) suppliedby Ferro Co. having 0.54M LiTFS, 0.36M LiPF₆, and 0.025% by weightLiClO₄ salts were tested. The LiClO₄ salt was added to the electrolyteto suppress corrosion of aluminum. For comparison, ten 2430 coin cellsfilled with an electrolyte (battery grade) supplied by Ferro Co. having1 M LiPF₆ were also tested. Ten 2430 coin cells filled with anelectrolyte (battery grade) supplied by Ferro Co. having 0.64M LiTFS and0.025% by weight LiClO₄ salts were used as control cells.

As shown in FIG. 5, the cells including 0.54M LiTFS, 0.36M LiPF₆, 0.025%by weight LiClO₄ salts and 1 M LiPF₆ salt exhibited better performancerelative to the control cells. Efficiency was calculated as a ratio ofdelivered capacity to a theoretical capacity. Corresponding performancedata for different voltage cutoffs (VCO) are presented in Table 4.

TABLE 4 Efficiency, % Efficiency, % Electrolyte (1.7 VCO) (1.5 VCO)0.64M LiTFS, 0.025% by weight 36.35 39.12 LiClO₄ 0.54M LiTFS, 0.36MLiPF₆, 44.56 47.79 0.025% by weight LiClO₄ 1M LiPF₆ 57.25 60.38

EXAMPLE 5

Referring to FIG. 6, a graph showing voltage under highest current loadversus efficiency for stored (20 days@ 60° C.) coin cells having analuminum screen as a cathode current collector under the HEC (60 mApulse) simulation test is shown.

Test cells including LiTFS/LiPF₆/LiClO₄ salts were compared with testcells including LiTFS/LiClO₄ salts and test cells including LiPF₆ salt.Ten 2430 coin cells filled with an electrolyte (battery grade) suppliedby Ferro Co. having 0.54M LiTFS, 0.36M LiPF₆, and 0.025% by weightLiClO₄ were tested. The LiClO₄ salt was added to the electrolyte tosuppress corrosion of aluminum. For comparison, ten 2430 coin cellsfilled with an electrolyte (battery grade) supplied by Ferro Co. having1M LiPF₆ salt were also tested. Ten 2430 coin cells filled with anelectrolyte (battery grade) supplied by Ferro Co. having 0.64M LiTFS and0.025% by weight LiClO₄ were used as control cells. After assembly, thecells were stored for 20 days in a dispatch oven at 60° C.

As shown in FIG. 6, the cells including 0.54M LiTFS, 0.36M LiPF₆, 0.025%by weight LiClO₄ salts exhibited better performance relative to thecontrol cells. Cells filled with the 1M LiPF₆ salt electrolyte exhibitpoor performance (0 pulses) after storage. Efficiency was calculated asa ratio of delivered capacity to a theoretical capacity. Capacityretention was calculated as a ratio (%) of performance efficiency afterand before storage. Corresponding performance data for different voltagecutoffs (VCO) are presented in Table 5.

TABLE 5 Efficiency, Efficiency, Capacity Capacity % % Retention, %Retention, % Cell # (1.7 VCO) (1.5 VCO) (1.7 VCO) (1.5 VCO) 0.64M LiTFS33.70 37.85 92.7 96.8 and 0.025% by weight LiClO₄ 0.54M LiTFS, 43.8647.23 98.4 98.8 0.36M LiPF₆, 0.025% by weight LiClO₄ 1M LiPF₆ 0 0 0 0

EXAMPLE 6

Referring to Table 6, the capacity retention of test cells after storagefor 20 days at 60° C. is shown. Table 6 also shows performance data fortest cells under the digital camera test at room temperature.

Test cells including LiTFS/LiPF₆ salts with relatively low cathodemoisture content were compared with test cells including LiTFS/LiTFSIsalts with relatively low cathode moisture content, and test cellsincluding LiTFS/LiPF₆ salt with relatively high cathode moisturecontent. Ten 2/3A cells filled with an electrolyte (battery grade)supplied by Ferro Co. having 0.54M LiTFS and 0.36M LiPF₆ salts weretested. The cathode moisture content for these cells was in the range of400-600 ppm. Ten 2/3A control cells filled with an electrolyte (batterygrade) supplied by Ferro Co. having 0.54M LiTFS and 0.36M LiTFSI saltswere also tested. The cathode moisture content for the control cells wasin the range of 400-600 ppm. Ten 2/3A cells assembled with relativelyhigher moisture (HM) cathodes (cathode moisture content is in the range1000-1500 ppm) and filled with an electrolyte (battery grade) suppliedby Ferro Co. having 0.54M LiTFS and 0.36M LiPF₆ salts were also tested.After assembly, the cells were stored for 20 days in a dispatch oven at60° C.

As shown in Table 6, after storage, the cells assembled with 400-600 ppmof moisture and 1000-1500 ppm of moisture including 0.54M LiTFS, 0.36MLiPF₆ electrolyte exhibited capacity retention, compared to the controlcells. Capacity retention was calculated as a ratio (%) of deliveredcapacity after and before storage.

TABLE 6 Capacity Capacity Capacity (Fresh) (Stored) Retention TestElectrolyte Cycle Ah Cycle Ah (%) RT, 2.0 V 0.54M LiTFS, 0. LiTFSI 1300.892 123 0.847 95.0 0.54M LiTFS, 0.36M LiPF₆ 135 0.921 120 0.830 90.10.54M LiTFS and 0.36M LiPF₆, HM 116 0.806 107 0.745 92.4 RT, 1.7 V 0.54MLiTFS, 0.LiTFSI 161 1.131 153 1.077 95.2 0.54M LiTFS, 0.36M LiPF₆ 1631.136 150 1.064 93.7 0.54M LiTFS and 0.36M LiPF₆, HM 147 1.047 140 0.99094.6 RT, 1.5 V 0.54M LiTFS, 0.LiTFSI 168 1.182 162 1.147 97.0 0.54MLITFS, 0.36M LiPF₆ 168 1.180 159 1.132 95.9 0.54M LiTFS and 0.36M LiPF₆,HM 154 1.103 150 1.078 97.3

All publications, patents, and patent applications referred to in thisapplication are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

Other embodiments are within the claims.

1. A primary electrochemical cell, comprising: a cathode comprising acathode active material consisting of manganese oxide and/or irondisulfide, the cathode having less than about 2,000 ppm of water; acathode current collector comprising aluminum; an anode comprisinglithium; and an electrolyte comprising lithiumtrifluoromethanesulfonate, LiPF₆, and a third lithium salt selected fromthe group consisting of LiClO₄ and lithium-bis(oxalate) borate.
 2. Thecell of claim 1, wherein the cathode has less than 1,500 ppm of water.3. The cell of claim 1, wherein the cathode has less than 1,000 ppm ofwater.
 4. The cell of claim 1, wherein the cathode has less than 500 ppmof water.
 5. The cell of claim 1, wherein the electrolyte comprises, inmole fraction, from 20% to 80% of lithium trifluoromethanesulfonate andfrom 20% to 80% of LiPF₆.
 6. The cell of claim 1, wherein theelectrolyte comprises from about 300 to about 10,000 ppm of LiClO₄. 7.The cell of claim 1, further comprising an aluminum surface.
 8. The cellof claim 1, wherein the electrolyte further comprises a materialselected from the group consisting of ethylene carbonate, propylenecarbonate, dimethoxyethane, butylene carbonate, and dioxolane.
 9. Thecell of claim 1, wherein the electrolyte further comprises propylenecarbonate and dimethoxyethane.
 10. The cell of claim 9, wherein theelectrolyte comprises from about 30% to about 90% by weight ofdimethoxyethane.
 11. The cell of claim 9, wherein the electrolytefurther comprises ethylene carbonate.
 12. The cell of claim 11, whereinthe electrolyte comprises, by weight, from about 5% to about 30% ofethylene carbonate, and from about 30% to about 90% dimethoxyethane. 13.The cell of claim 1, wherein the electrolyte further comprises ethylenecarbonate, butylene carbonate, and dimethoxyethane.
 14. The cell ofclaim 13, wherein the electrolyte comprises, by weight, from about 5% toabout 30% of ethylene carbonate, and from about 30% to about 90% ofdimethoxyethane.
 15. The cell of claim 1, wherein the electrolytecomprises dioxolane.
 16. A method, comprising: discharging, only once, aprimary electrochemical cell comprising a cathode comprising manganeseoxide and/or iron disulfide, the cathode having less than about 2,000ppm of water, a cathode current collector comprising aluminum, an anodecomprising lithium, and an electrolyte comprising lithiumtrifluoromethanesulfonate, LiPF₆, and a third lithium salt selected fromthe group consisting of LiclO₄ and lithium-bis(oxalate) borate; anddisposing the cell without recharging the cell.